Unraveling tectonic inversion and wrench deformation in the Eastern Cordillera (Northern Andes) with paleomagnetic and AMS data

Abstract

Complex orogenic belts typically display internal variations in deformational style, as is the case of the northern Eastern Cordillera of Colombia, which changed abruptly into a regional strike-slip system in the NNW-striking Santander Massif. We report paleomagnetic data, anisotropy of magnetic susceptibility (AMS) data, and magnetic mineralogy from 47 sites distributed in the northern Eastern Cordillera and Santander Massif to investigate and compare: (1) variations in the intensity of the deformation, (2) magnitude and sense of vertical axes rotations, and (3) the character and effect of strike-slip displacements along the Bucaramanga fault and NE-striking transverse faults within the Santander Massif. Rock magnetic experiments show that hematite is the principal magnetization carrier in all these rocks. Rocks of the axial zone of the Eastern Cordillera show intermediate magnetic fabrics. Magnetic fabrics of rocks from the Santander Massif, and the western flank of the Eastern Cordillera, are uniformly oblate with preservation of sedimentary fabrics. Directions of the ChRM from sites in the Eastern Cordillera (30 accepted of 35 sites) are interpreted to indicate that the axial zone has not been rotated, whereas sites located along the western flank of the northern Eastern Cordillera yield data suggesting clockwise rotations, which increase in magnitude up to 90° in areas bounded by NE-striking transverse faults. In the Santander Massif (9 accepted of 12 sites) data suggest a mix of counterclockwise rotations (~30°) and clockwise rotations of ~40°. The inferred clockwise vertical-axis rotations in the northern Eastern Cordillera and Santander Massif of up to 45° are interpreted to be related to tectonic inversion of pre-existing Mesozoic age normal faults during the Neogene as right-lateral faults. Our corrected paleomagnetic inclination data are interpreted to support the hypothesis of northward translation of the studied tectonic elements during the Middle Jurassic to earliest Cretaceous time.